2001 Miata Won't Start

I am having an issue with a 2001 Miata with about 190K miles.

When I attempt to start the car I get nothing, no accessories, no ignition, nothing...

First thought was the battery or connections, but battery shows 12.5V across the terminals and the connections are tight and clean.

There were no issues leading up to the car not starting.  I parked it for the night the evening before, and was planning to drive it the morning after since it was going to be a nice day, but nothing happened.

Any suggestions on what I should be looking at?

Check the other end of the ground wire. It's only like a foot long. 

Main relay usually fails like this, but it won't take out the accessories. Not even a crank? It's hard to stop them from cranking.

If you have B+ at the ignition switch, then it's probably the ignition switch. If you don't, then go upstream until you do.

"Connections are tight and clean" as in you just cleaned and tightened them, or as in they look good?

I'll grant you, it seems very unlikely to go from "fine" to "nothing" like that, but too many troubleshooting sessions have gone too long because things get ruled out without testing.

If you’re getting nothing, one of the connections isn’t right or isn’t clean.  I second Stampie’s suggestion of double checking the ground(s). 

Whenever I have a completely dead vehicle, I'll pull a measurement from the starter battery connection (pop the right front wheel off) to the frame/engine.   That'll tell you if your main electrical circuit is actually energized.  That'll give you a direction.  If it's no bueno, then you need to start at the battery terminals and follow the cables until you find the break.  

If you have power at the starter, then do what Keith suggests and look at your key cylinder (or the connector to it).

12.5V is OK but not great. Have you tried to measure the voltage at the battery while someone tries to crank the car?

Or the other question is did you lose an ignition switch? I've had it happen the other way. Turn the key and nothing at all happens. Everything looks good and seems tight but turning the key does nothing at all. Test out the ignition switch and it's an open circuit. Not as common as it use to be but make sure you check out both ends.